1. Field of the Invention
The invention relates to a microchip measurement device.
2. Description of Related Art
In various fields such as medical treatments, biology and the like, a process has recently been under increasing development which is called μ-TAS (μ-Total Analysis System) or “Lab on a chip” and in which analyses are performed with high precision and high sensitivity using a microchip and substances are synthesized with high efficiency. For example, μ-TAS is a device in which chemical processes such as pumping, mixing, injections, reactions, extractions, analyses and the like are integrated into one microchip. Since this device can carry out chemical reactions which cannot be performed in chemical facilities with ordinary scales, with high efficiency, it has a potential to become an important tool for carrying out everyday health check-ups and injections and therapies with consideration of different individual body compositions.
In a microchip analysis system, to measure the concentration of a component to be detected in a test object liquid (hereinafter also called “liquid to be tested”), generally a process for analysis of decadic extinction [i.e., absorbance] is used.
In an analysis of decadic extinction, based on the obtained decadic extinction, the concentration of the component to be detected in the liquid to be tested is computed. Such a microchip measurement device is described, for example, in Japanese patent disclosure document JP 2004-109099 A.
In the above described microchip analysis system, the wavelength range of the radiated light differs according to the component to be analyzed. Therefore, in the case of a light source which emits a single wavelength, such as a laser, the substance to be analyzed is limited. In order to achieve versatility, it is advantageous to use a light source which can change the wavelength of the light to be emitted according to the substance to be analyzed and which emits light with a wide wavelength range.
Therefore, a lamp can be imagined as the light source which, for example, emits light with a wide emission spectrum. In particular, a short arc lamp is also advantageous with respect to the focusing property since it has high radiance and is a point light source.
FIG. 8 schematically shows the optical system of a microchip analysis system. In the figure, a short arc lamp 10 emits light that is converted via given optical elements 11, 12 into parallel light, moreover, with wavelengths being extracted only in a given range and being incident in a chip holder 20. The light incident in the chip holder 20 passes through an aperture 20A and is incident in the incidence surface 21a of the measurement part 21A of the microchip 21. The light which is transmitted by the liquid which is to be tested and with which the measurement part 21A is filled is incident in a photodiode 31 as a light receiving element. An amplifier 32 is connected to the light receiving element 31. The data, after amplification of the light quantity, are recorded in a recording means, such as a data logger 33 (automatic recording means or the like). After a given measurement interval has passed, in an operation part (not shown), measurement data are analyzed and the decadic extinction is computed. The data of the quantity of light are determined by a control element (not shown) during a given decadic extinction measurement interval, for example, with an interval of 1 second.    (Patent document 1) Japanese patent disclosure document 2004-109099    (Patent document 2) Japanese patent disclosure document 2003-107094    (Patent document 3) Japanese patent disclosure document 2005-040784 corresponding to U.S. Patent Application Publication US2005006372.
In a discharge lamp of the short arc type, there are cases in which the phenomenon of an arc jump occurs towards the end of the lamp service life. When the phenomenon of an arc jump occurs, the position of the arc formed between the electrodes fluctuates. When an arc jump occurs, the flow of thermions which have flowed in the same path region temporarily changes its path region, by which resistances and the voltage shift and the quantity of light are likewise increased or reduced. When arc jump occurs, and the quantity of light emitted from the lamp does not stabilize, even for a small change in the quantity of light major influences are exerted on the measurement of the microchip because the cross-sectional area of the light incidence part which is formed in the microchip is, for example, 1 mm×1 mm, i.e., is extremely small.
As a correction means, it can be imagined that the fluctuation between the quantity of light prior to light incidence in the microchip and the quantity of light after passage (light exit) is monitored. Since control of the optical axis is very difficult in practice and in addition costs are high, implementation is however difficult.